1. Field of the Invention
The present invention relates to a method and a system for distributing of user equipment context in an evolved packet system, comprising a plurality of user equipment, at least one eNodeB, at least a first mobility management entity and a second mobility management entity and at least one serving gateway connected to at least a first and a second mobility management entity, wherein the plurality of user equipment is connected via one of the eNodeBs to a second mobility management entity and to the at least one serving gateway, wherein the user equipment context for the plurality of user equipment is each stored at the second mobility management entity.
2. Description of the Related Art
Long term evolution (LTE) as mobile communication standard generally provides higher download capabilities for mobile user equipment compared with the former UMTS-standard. However, with the advent of new features like Machine-Type Communication, for example laid down in standard 3GPP TS 22.368, “Service requirements for Machine-Type Communications (NATO); Stage 1”, the amount of context data to be stored in the core network ON is increased while at the same time the relationship between the amount of signaling and the amount of data traffic is changed: For example machine-type communication due to low data volume, infrequently active and low mobility type of user equipment occurs.
In FIG. 1, a conventional evolved packet system architecture is shown which is simplified only showing relevant entities with regard to the present patent application. A user equipment UE is connected to an evolved Node B which is located in a Radio Access Network RAN. The evolved Node B (eNB) is connected via interface S1-MME to the mobility management entity MME located in the core network CN related to the control plane and via S1-U interface to a serving gateway SGW also located in the core network CN related to the user plane. The mobility management entity MME is connected via interface S11 to the serving gateway SGW. The eNB is the radio base station in the Radio Access Network RAN. The eNB or more general the eNBs distribute initial requests of the user equipment (e.g. for attachment) according to the Network Node Selection Function NNSF in the Radio Access Network RAN, for example as laid down in standard 3GPP TS 36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2.”.
For initial events when no so-called user equipment context is yet stored, meaning that the user equipment is not known to a mobility management entity, these decisions are typically based on load considerations, including also explicit overload indications by mobility management entities (MME). After an initial request by the user equipment has been accepted by the mobility management entity for this user equipment, the user equipment context is created and stored in the mobility management entity MME. It is maintained in the mobility management entity MME as long as the user equipment UE remains attached or roams to an area where a corresponding evolved Node B (eNB) has only connectivity with another mobility management entity. In this case the user equipment context is transferred from the old mobility management entity to the new mobility management entity during a Tracking Area Update (TAU) in idle mode. or within a handover procedure in active mode.
In the evolved packet system the user equipment receives a temporary identifier, the so called Global Unique Temporary Identity GUTI, which is related to the mobility management entity storing the user equipment context data. The mobility management entity identification is part of the Global Unique Temporary Identity GUTI. If the Global Unique Temporary identity (GUTI) is changed this affects the user equipment and requires a signaling between the core network (CN), respectively a corresponding device or entity in the core network, and the user equipment (UE). The following relations hold, wherein “+” is to be understood as concatenation:
GUTI GUMMEI M-TMSI Global Unique Temporary (UE) Identifier
GUMMEI=MCC+MNC+MME1 Global Unique MME identifier
MMEI=MMEGI+MMEC MME identifier
S-TMSI=MEC+M-TMSI epS-Temporary Mobile Subscriber identity
M-TMSI Mme-Temporary Mobile Subscriber Identity
In conventional evolved packet system an exchange of user equipment contexts between different mobility management entities is only possible in a reactive manner. Another disadvantage is that in this case a new temporary identifier has to be allocated for the user equipment, involving signaling with the user equipment.